Replace the 3rd of a chord with a 2nd or 4th. Instead of C-E-G, play C-D-G (Csus2). Instead of G-B-D, play G-C-D (Gsus4). This adds "longing" and tension.
There are several comprehensive PDF guides specifically featuring approximately 400 chord progressions or variations that you can download for free or view online. 400+ Chord Progression PDFs 400 Piano Chord Progressions (Scribd) 400 piano chord progressions pdf free
Note: The links provided above are sourced from public search results and are available for free download/viewing. Happy Birthday Chord Progressions Guide | PDF - Scribd Replace the 3rd of a chord with a 2nd or 4th